Recently, active and intensive studies of fuel cells as next-generation energy sources have been conducted since fuel cells are pollution-free clean energy sources so that they can substitute for other existing energy sources. The basic concept of a fuel cell is the use of electrons generated by the reaction of hydrogen with oxygen. A fuel cell is defined as a cell capable of producing direct current by converting chemical energy, derived from a chemical reaction of fuel gas including hydrogen with an oxidant including oxygen, directly into electric energy. Unlike other conventional batteries, fuel cells generate electricity by utilizing fuel and air supplied from the exterior. Fuel cells may be classified depending on drive conditions into phosphoric acid fuel cells, alkaline fuel cells, proton exchange membrane fuel cells, molten carbonate fuel cells, direct methanol fuel cells and solid electrolyte fuel cells. Particularly, proton exchange membrane fuel cells (PEMFC) have a high energy density and can be used at room temperature, and thus have been in the spotlight as portable electric power sources.
In a proton exchange membrane fuel cell (PEMFC), protons generated in the anode are transferred to the cathode through a polymer electrolyte membrane, thereby forming water via the bonding of oxygen and electrons. A PEMFC utilizes the electrochemical energy generated at this time. Because a PEMFC is driven at a low temperature, it shows a relatively low efficiency when compared to other fuel cells. Therefore, platinum-supported carbon is generally used as a catalyst in a PEMFC in order to increase the efficiency of the fuel cell. In fact, use of a platinum-supported carbon catalyst provides a fuel cell with a markedly improved quality when compared to fuel cells using other metal-supported catalysts.
However, because platinum supported on a support of the platinum-supported carbon used as a catalyst for a proton exchange membrane fuel cell merely has a size of several nanometers, the catalyst is unstabilized as electrochemical reactions proceed and coarsening of platinum nanoparticles occur. Such coarsening of platinum nanoparticles gradually causes a drop in surface area of platinum nanoparticles required for the reactions. This also adversely affects the quality of a fuel cell.